1. Field of the Invention
This invention relates to a conducting roller assembly for an electroplating apparatus, which processes a workpiece that is shaped as a horizontal plate, more particularly to a conducting roller assembly, which includes two rows of equidistant conducting posts that are in electrical connection with two opposite sides of a conducting roller.
2. Description of the Related Art
During an electroplating operation, a cathode current is generally transmitted from a power supply to a workpiece via two conducting rollers, which are arranged one above another so as to clamp and move the workpiece therebetween. Referring to FIG. 1, a conventional conducting roller 7 is shown to include a rotatable conductive roller body 71 that presses against a side surface of a workpiece 8 (see FIG. 2), such as a horizontal circuit board, and a stationary conducting rod 72 that is inserted into a chamber 711 in a left end portion of the roller body 71. The chamber 711 has two ends 712, 713, which are provided with a pair of bearing members 714, on which the conducting rod 72 is journalled. The roller body 71 is rotated by means of a gear unit 715. An annular seal 73 is sleeved on the conducting rod 72 so as to seal the chamber 711. A conductive liquid 74 is filled in the chamber 711 between the roller body 71 and the conducting rod 72. As such, electric current can be transmitted from the conducting rod 72 to the roller body 71 via the conductive liquid 74. The disadvantages of the conducting roller 7 are as follows:
(1) Referring to FIG. 2, a resistance loss is incurred by the conducting roller 7, and increases gradually from the left end 721 to the right end 716 in view of the condition that only a single cathode current input is provided at the left end 721 of the roller body 71. For example, assuming that the voltage is 2 volts, according to Ohm""s law I (current)=V (voltage)/R(resistance),
when R1 is 0.1 (ohm), current is 20 amperes;
when R2 is 0.15, current is about 13.3 amperes;
when R3 is 0.2, current is 10 amperes;
when R4 is 0.25, current is 8 amperes;
when R5 is 0.3, current is about 6.7 amperes;
when R6 is 0.35, current is about 5.7 amperes;
when R7 is 0.4, current is 5 amperes; and
when R8 is 0.45, current is about 4.4 amperes.
xe2x80x83As such, the current difference between the left and right ends 721, 716 of the conducting roller 7 is relatively large, thereby resulting in an uneven thickness of metal coating on the circuit board 8. Furthermore, in order to reduce both the resistance loss and the current difference between the ends 721, 716 of the conducting roller 7 so as to maintain the thickness difference of the metal coating within an acceptable range, the length of the conducting roller 7 is limited such that the conducting roller 7 is not suitable for processing a comparatively wide workpiece.
(2) The conductive liquid 74 is normally made of mercury, which is highly poisonous, thereby resulting in serious environmental protection problems caused during filling and disposal thereof.
An object of this invention is to provide a conducting roller assembly for an electroplating apparatus, which includes rows of equidistant conducting posts that will not result in any environmental protection problem and that can transmit a cathode current evenly to a plate-shaped workpiece, thereby forming an even thickness of metal coating on the workpiece.
According to this invention, a conducting roller assembly for an electroplating apparatus includes two conducting rollers arranged one above another so as to clamp and move a plate-shaped workpiece therebetween. The rollers are disposed intimately over one of two conducting members, and under the other one of the members. Each of the members is connected to two opposite sides of the respective one of the rollers by means of two horizontal rows of equidistant conducting posts. Each of the posts has one end that is fixed to and that is in electrical connection with a respective one of the members, and another end that is biased to contact the respective one of the rollers so as to establish an electrical connection between the respective one of the members and the respective one of the rollers. As such, electric current can be transmitted evenly to the rollers via the posts.